moles transform into quails (second climate of the third month)
A set phrase from the traditional 七十二候 calendar, marking the seasonal micro-climate when moles are said to turn into quails. Used only in historical or poetic contexts.
See also: 七十二候
One of the 72 micro-seasons is the phrase 'moles transform into quails'.
The 72 micro-season calendar system of which this phrase is a part; 田鼠化して鶉となる is one specific climate name within it.
A fixed expression from the classical Chinese calendar system 七十二候, adopted into Japanese. The exact origin of the mole-to-quail belief is uncertain, but it reflects ancient seasonal folklore.